--- SPI_Flash.c.orig	2022-02-28 16:36:53.000000000 +0900
+++ SPI_Flash.c	2023-01-12 17:16:23.097970598 +0900
@@ -69,11 +69,13 @@ static inline void spi_flash_enable(void
 	GPIO_PinInit(GPIO_SPI_FLASH_DO_U, Pin_SPI_FLASH_DO_U, &pin_config_output);
 	GPIO_PinInit(GPIO_SPI_FLASH_CS_U, Pin_SPI_FLASH_CS_U, &pin_config_output);
 	GPIO_SPI_FLASH_CS_U->PCOR = 1U << Pin_SPI_FLASH_CS_U;
+	__DSB();
 }
 
 static inline void spi_flash_disable(void)
 {
 	GPIO_SPI_FLASH_CS_U->PSOR = 1U << Pin_SPI_FLASH_CS_U;
+	__DSB();
 	GPIO_PinInit(GPIO_SPI_FLASH_CS_U, Pin_SPI_FLASH_CS_U, &pin_config_input);
 	GPIO_PinInit(GPIO_SPI_FLASH_DO_U, Pin_SPI_FLASH_DO_U, &pin_config_input);
 }
@@ -83,7 +85,7 @@ static inline uint8_t spi_flash_transfer
 	for (uint8_t bit = 0; bit < 8; bit++)
 	{
 		GPIO_SPI_FLASH_CLK_U->PCOR = 1U << Pin_SPI_FLASH_CLK_U;
-		//		__asm volatile( "nop" );
+		__DSB();
 		if ((c & 0x80) == 0U)
 		{
 			GPIO_SPI_FLASH_DO_U->PCOR = 1U << Pin_SPI_FLASH_DO_U;// Hopefully the compiler will optimise this to a value rather than using a shift
@@ -92,13 +94,12 @@ static inline uint8_t spi_flash_transfer
 		{
 			GPIO_SPI_FLASH_DO_U->PSOR = 1U << Pin_SPI_FLASH_DO_U;// Hopefully the compiler will optimise this to a value rather than using a shift
 		}
-		//		__asm volatile( "nop" );
+		__DSB();
 		c <<= 1;
 		c |= (GPIO_SPI_FLASH_DI_U->PDIR >> Pin_SPI_FLASH_DI_U) & 0x01U;
 		// toggle the clock
 		GPIO_SPI_FLASH_CLK_U->PSOR = 1U << Pin_SPI_FLASH_CLK_U;
-		//		__asm volatile( "nop" );
-
+		__DSB();
 	}
 	return c;
 }